Science! It Works! Gravitational Waves in the Cosmic Microwave Background

And I am really, really sad that I will never understand this. I mean, I have derived the precession of the perihelion of Mercury and calculated the energy states of a particle trapped in a box. But with this stuff I am lost...

the BICEP2 experiment has purportedly detected signs of gravitational waves in the polarization of the cosmic microwave background radiation. If it’s true (and the result holds up), it will be an enormously important clue about what happened at the very earliest moments of the Big Bang....

Punchline: other than finding life on other planets or directly detecting dark matter, I can’t think of any other plausible near-term astrophysical discovery more important than this one for improving our understanding of the universe. It would be the biggest thing since dark energy....

Cosmic inflation is actually a pretty simple idea. Very early on–we’re not sure exactly when, but plausibly 10-35 seconds or less after the Planck time–the universe went through a phase of accelerated expansion... to smooth things out: stuff like density perturbations, spatial curvature, and unwanted relics just get diluted away. Then at some point–again, we aren’t sure when or why–this period ends, and the energy that was driving the accelerated expansion converts into ordinary matter and radiation, and the conventional Hot Big Bang story begins. Except that quantum mechanics says that we can’t completely smooth things out. The Heisenberg uncertainty principle tells us that there will always be an irreducible minimum amount of jiggle.... So inflation makes certain crude predictions... the universe is roughly homogeneous, and the curvature of space is very small. But the perturbations on top of this basic smoothness provide more specific, quantitative information.... There are two types of perturbations we expect to see, based on two kinds of light quantum fields that fluctuated... the “inflaton”... that eventually converts into matter and radiation... [and] produce[s] fluctuations in the density of the early plasma.... These are what we have already seen in the Cosmic Microwave Background (CMB)... differences in temperature from point to point in the CMB, and it’s these small difference (about one part in 105) that grow into stars, galaxies and clusters.... Then... there are... gravitational waves, or “gravitons”.... Just as an electromagnetic wave is an oscillation in the electric and magnetic fields... a gravitational wave is an oscillation in the gravitational field....

Gravitational waves from inflation are interesting for a couple of reasons. First, we know they should be there.... Second, there is a way to disentangle the gravitational waves from the density fluctuations, using the polarization of the CMB.... How strong the gravitational waves are at different wavelengths reveals a great deal about the details of inflation — including one magic number, the energy density of the universe during the inflationary era....

We can distinguish density-induced polarization (“scalar modes”) from gravitational-wave-induced polarization (“tensor modes”) by the shape of the polarization pattern on the sky.... you can decompose it into what are called E-modes and B-modes.... B-modes have a net twist to them.... In straightforward models of inflation, the amplitude of the gravitational waves is directly proportional to the inflationary energy scale. If this rumored measurement (and the inflationary interpretation) are correct, we would have data about a physical process just a bit below the Planck scale. Currently, our empirical knowledge of the early universe only stretches to about one second after the Big Bang, courtesy of primordial nucleosynthesis. Here we’re talking about pushing that to less than 10-35 seconds....

More importantly than the prospects for any given model, however, this is great news for inflation itself. While it’s the starting point for much contemporary cosmological theorizing about the early universe, honest physicists are quick to admit that inflation has its conceptual problems. The prediction of gravitational waves is one of the strongest empirical handles we have on whether inflation actually happened, so if this result is announced like the rumors say (and it holds up) it will dramatically effect how we think about the earliest moments in the history of our universe...

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Science! It Works! Gravitational Waves in the Cosmic Microwave Background

And I am really, really sad that I will never understand this. I mean, I have derived the precession of the perihelion of Mercury and calculated the energy states of a particle trapped in a box. But with this stuff I am lost...

the BICEP2 experiment has purportedly detected signs of gravitational waves in the polarization of the cosmic microwave background radiation. If it’s true (and the result holds up), it will be an enormously important clue about what happened at the very earliest moments of the Big Bang....